N-Acetyl-d-glucosamine (GlcNAc) was treated in subcritical fluids with ethanol contents of 0% –80% (w/w) using a tubular reactor at 190℃. The disappearance of GlcNAc in all the aqueous ethanol fluids obeyed first-order kinetics, and the rate constant was roughly proportional to the water molarity of the aqueous ethanol; this indicates that water plays an important role in the disappearance of GlcNAc. The pH of the reaction mixture decreased as the reaction proceeded and then plateaued because of the formation of a buffer system by glucosamine and the acetic acid liberated from GlcNAc. The ultraviolet absorption spectra of the reactor effluents suggested the formation of both carboxylic acids and furfurals. The formation of furfurals and color development were suppressed at higher ethanol contents.
A method to objectively evaluate the external quality of broccoli heads using a computer vision system (CVS), a type of digital camera, was proposed. The CVS was effective in calculating the spatial distribution of color space values of broccoli heads. Value of –a*/b* (chromaticity of Commission Internationale de l’Éclairage) was effective in evaluating the concentration of chlorophyll a. An –a*/b* value greater than 0.94 indicated fresh buds that remained green. Conversely, the value of a* was effective in evaluating the existence of anthocyanins that damage the external quality of the broccoli head. Buds with low concentrations of anthocyanin had an a* value less than -12. These two thresholds were used for visualizing high-quality buds with high concentrations of chlorophyll a and low concentrations of anthocyanin. The proportion of high-quality buds of typical heads that included low or high concentrations of anthocyanin reduced from 39% or 22% to 15% or 5.4% during 5 d storage. The proportion of high-quality buds of typical heads with low anthocyanin concentrations was usually higher than those with high anthocyanin concentrations. These results suggest that the proposed method using the CVS is suitable for objectively evaluating the external quality of broccoli heads and selecting high-quality heads.
A model to identify the effective diffusivity and to predict the drying kinetics during non-isothermal convective drying of yellow passion fruit (Passiflora edulis Sims f. flavicarpa Degener) seeds was formulated and validated. The governing equations for coupled mass and heat transfer phenomena were expressed in a generalized coordinate system in order to obtain a one-dimensional model suitable for the non-regular geometry of the seeds. Solid shrinkage, moisture and temperature-dependent transport properties, convection heat and mass transfer at the seed surface and symmetrical distribution of moisture content and temperature inside the material were considered. To identify the moisture effective diffusivity, model estimations were fitted to data from drying experiments carried out at air temperatures of 40, 50, and 60℃ and at air velocities of 0.6 and 1.4 m·s−1. The air velocity promoted a lower effect than the air temperature on drying rate, suggesting the internal resistance to mass transfer controlled the water diffusion. The proposed model could contribute to understand the diffusion mechanisms in the material, offering an alternative approach to study the convective drying of non-regular particles due to it requires a simpler solving process and a shorter calculation time than some multidimensional approaches.
The objective of this research was to find the industrially-accepted processing method of the currently underutilized wet grape pomace prior to subsequent extraction of natural ingredients. Due to high moisture content (2.5-3.0 kg/kg db), thermal drying of pomace is an expensive and time-consuming operation. Therefore, the energy efficiency of non-thermal electrohydrodynamic (EHD) technology as applied for grape pomace drying was extensively studied. The experiments on EHD drying at temperature 20℃ revealed excellent quality of the dry product. Superior energy efficiency of the EHD drying ranging from 600 to 1580 kJ per kg of evaporated water as reported in topical literature was confirmed in our experimental study. These preliminary experiments on the lab-scale showed benefits of EHD drying of heat-sensitive grape pomace to be further transformed into food additives, skin powder and grape oil.
Sorption isotherms aid the analysis of different classes of water to determine the energy required to remove this moisture from seeds. The goal of the present study was to determine and analyze the sorption isotherms for barley seeds. Qualitative and quantitative thermodynamic analysis was performed by GAB model parameters and by calculating the net isosteric heat and differential entropy of sorption. The GAB model successfully described the experimental data. The monolayer equilibrium moisture decreased from 0.092 kg·kg-1 to 0.057 kg·kg-1 as the temperature increased from 15 to 50℃. The net isosteric heat of sorption for the monolayer calculated by the GAB equation parameters exhibited good agreement with that calculated by the Clausius-Clapeyron equation, with values of 2433.0 and 2233.7 kJ·kg-1, respectively. Environmental conditions may have affected the formation of the adsorption sites within the seeds endosperm when compared with literature data. The use of empirical models to fit sorption isotherms may mischaracterize the thermodynamic analysis of the monolayer.
The demand to increase food production to feed the growing number of the world population is becoming a primary concern for everyone. At the same time, one-third of the food produced is lost or wasted globally. The food wastes and the by-products of the food production and processing operations still have nutritional ingredients in them suitable for human consumption. To encounter this issue, drying methods can be carried out to add value to food waste, prolong the product’s shelf life and thus provide more food products. Integrated microwave drying systems have the potential to produce dehydrated products from the food waste. In this paper, integrated osmotic dehydration with microwave-assisted hot air drying method is described for the development of dehydrated broccoli stalk product. The techno-economical aspects in terms of raw material availability, process design, energy input, capital inputs, operation costs and environmental benefits are also discussed. This integrated microwave drying concept will be of use to process other biological materials that have the potential at the marketplace.